It is becoming common for whole blood collected from a donor to be separated into blood component preparations, such as an erythrocyte preparation, a thrombocyte preparation, and a blood plasma preparation, stored and then provided for transfusion. Since microaggregates and leukocytes included in these blood preparations cause various side effects of blood transfusion, many methods of removing these undesirable components before transfusion and then performing transfusion, or of removing these undesirable components after blood collection, temporarily storing the preparations, and then providing the preparations for transfusion have been widely used.
Among methods of removing these undesirable components from blood preparations, processing blood preparations through a blood processing filter is most typical. Two types of blood processing filters are used; one is what includes a filter element made of nonwoven fabric or a porous body equipped in, for example, a flexible container as described in Patent Literatures 1 to 5, and the other is what includes the filter element equipped in a hard container made of polycarbonate or the like.
Typically, for processing of a blood preparation through a blood processing filter, a blood preparation bag containing the blood preparation to be processed is connected to an inlet of the blood processing filter, the blood preparation bag is placed at a position higher than the blood processing filter by approximately 20 to 100 cm. As a result, the blood preparation is introduced from the blood preparation bag into the blood processing filter by the action of gravity. Meanwhile, a recovery bag for accommodating the filtered blood preparation is connected to an outlet of the blood processing filter. The recovery bag is placed at a lower position by approximately 50 to 100 cm than that of the blood processing filter. As a result, the filtered blood preparation is collected in the recovery bag by the action of gravity. At this time, a pressure loss occurs due to the resistance of the filter element, in an inlet-side space in the blood processing filter container with respect to the filter element, whereby the space becomes a positive pressure. On the contrary, in an outlet-side space with respect to the filter element, the blood preparation flows from the outlet, whereby the space becomes a negative pressure.
Since a blood processing filter with a flexible container as shown in Patent Literatures 1 to 5 has a container that is flexible, the container swells like a balloon due to a positive pressure in an inlet-side space, and the filter element is pressed against on the outlet side of the container. On the other hand, in an outlet-side space, the container is in close contact with the filter element due to a negative pressure, and the state is brought into that where the opening of the outlet is blocked. That is, since blood tends to flow from the filter but the opening is blocked, it is difficult for the blood to flow out.
On the contrary, a blood processing filter with a hard container does not largely deform even during filtration, the filter element is not pressed against the outlet-side, and the state is not brought into that where the opening of the outlet is blocked. Such a hard container includes an inlet-side container element and an outlet-side container element which are fitted with each other, and rib-shaped convexes provided for the inlet-side container element and the outlet-side container element are pressed against each other, thereby clamping the outer edge portion of the filter element. By pressing the convexes against each other to a high density, the side leakage (side flow) where blood flows over the outer edge portion of the filter element without being filtered can be prevented.
Incidentally, the entire apparatus is required to be sterilized in order to be used for processing blood preparations. Typically, steam sterilization is applied. The filter for the hard container has a poor steam permeability, and is required to be subjected to a long sterilization time. However, execution of a long-time autoclave sterilization causes degradation of blood stock solution and the like. Accordingly, after the filter is sterilized in a separated manner and the blood bag, circuit and the like are then connected, sterilization is required to be performed again. Thus, complicated operations are required to be executed.
A filter described in Patent Literature 6 has been invented as means for solving this. In this filter, a part of or the entire inlet-side container element is made of a flexible member, and a part of or the entire outlet-side container element is made of a hard member. In this filter, adoption of the hard member for the outlet-side container element can prevent a poor blood flow due to close contact of the outlet-side container element with the filter element, while adoption of the flexible member for the inlet-side container element can secure steam permeability during steam sterilization.